A new study published in the journal Science is suggesting that 66 per cent of contracting cancer is purely based on (bad) luck. The other two mitigating factors, lifestyle/environment and genetics, account for 29 per cent and five per cent, respectively.
Scientists at the Johns Hopkins Kimmel Cancer Centre examined DNA sequencing and epidemiologic data from around the world to come to their findings. They suggest that the genetic mutations that develop into cancer are a result of random errors that take place when cells naturally replace themselves.
“It is well-known that we must avoid environmental factors such as smoking to decrease our risk of getting cancer,” study co-author, Cristian Tomasetti, said in a statement.
“But it is not as well-known that each time a normal cell divides and copies its DNA to produce two new cells, it makes multiple mistakes. These copying mistakes are a potent source of cancer mutations that historically have been scientifically undervalued, and this new work provides the first estimate of the fraction of mutations caused by these mistakes.”
The researchers say that people still need to be vigilant about their lifestyle habits — avoiding smoking and other carcinogenic environments, including excess sun exposure — however, these findings also provide cancer patients who were always diligent about their health, and parents of cancer-stricken children, with peace of mind knowing that their diagnosis isn’t their fault.
“Nothing you did or didn’t do was responsible for your illness,” co-author, Bert Vogelstein, said.
This study comes two years after another one conducted by the duo that drew the first correlation between DNA copying errors and cancer. It used a mathematical model to estimate the number of stem cells in the tissues where 31 different cancers were detected (including colon and brain) and estimated the rate at which the cells divided. This helped them determine why certain cancers, like colon, occur more frequently than brain cancer.
The new study, however, used a different mathematical model to examine genome sequencing and epidemiologic data from 32 different cancers. The researchers deduced that it takes two or more gene mutations to form cancer, and these mutations could be the result of DNA copying errors, the environment or inheritance.
In the case of pancreatic cancer, 77 per cent of cancerous cells are due to random DNA copying errors, 18 per cent are environmental factors and 5 per cent are inherited. For prostate, brain and bone cancers, 95 per cent are due to random copying errors.
However, in the case of lung cancer, 65 per cent of the mutations are due to environmental factors (mostly smoking) and 35 per cent are on account of DNA copying errors. This means healthy lifestyle choices still play a large part in preventing cancer.
If it takes a minimum of two gene mutations to form cancer, smoking, obesity or lack of exercise can kick the third cell mutation over the edge and into a diseased state.
While no expert would argue that lifestyle and environmental factors play a role in the development of cancer, Dr. Rob Nuttall, assistant director of health policy at the Canadian Cancer Society, does see a discrepancy in the numbers reported in this study.
“You can use what we know about cell divisions to explain cancer from a mathematical approach, but these numbers are different from what we’ve seen in real world evidence in the field of epidemiology,” he said to Global News. “What we see is that 50 per cent of cancer is preventable, and the other 50 per cent is due to things we have no control over.”
Nuttall says the No. 1 cause of cancer in Canada and around the world is smoking, and he points to leading a healthy lifestyle — having a healthy body weight, being active, eating well and limiting alcohol intake — as going a long way to lowering the risk of cancer.
He also stresses that there’s no time like the present to make those significant changes.
“Studies have shown that the time period after a person makes a change in their lifestyle habits [like quitting smoking or losing weight] results in an overall decline in the risk of getting cancer,” he said. “If you stop smoking, after 10 years, your risk goes down to almost the same level as a non-smoker. There’s a lot to be said for making a change now that will help you in the long run.”